Thermal switch having temperature sensitive pellet and movable contact



Dec. 13, 1966 P. E. MERRILL ETAL 3,291,945

THERMAL SWITCH HAVING TEMPERATURE SENSITIVE PELLET AND MOVABLE CONTACT Filed March 4, 1965 52 40F'G-6 FIG-7 3a LLIP N C. BARNETT IL ROBERT PLASKO hwm THEIR ATTORNEYS INVENTORS PHI DO M United States Patent THERMAL SWITCH HAVING TEMPERATURE SENSITIVE PELLET AND MOVABLE CON- TACT Phillip Edward Merrill, Don C. Barnett, and Emil Robert Plasko, all of Kettering, Ohio, assignors to Micro Devices Corp., Dayton, Ohio, a corporation of Ohio Filed Mar. 4, 1965, Ser. No. 437,210 2 Claims. (Cl. 200142) This invention relates to a fuse control, and particularly to a fuse control that may be of extremely small size.

One feature of this invention includes a fuse control of extremely small size but which can carry a relatively high current, and has a very high dielectric strength in comparison to its small size, and is capable of being manufactured in large quantities, and with a very simple method of manufacture.

Another feature of this invention includes a fuse of small size with a relatively large number of components, which may be assembled into a metallic casing which may have no insulative sleeve therein. Alternatively, such components may be assembled in a somewhat similar metallic casing in which an insulative sleeve may be placed, and which sleeve surrounds such components.

Other features of this invention become apparent from this description, the appended claimed subject matter, and the accompanying drawings, in which:

FIGURE 1 is an enlarged vertical cross section of one embodiment of this invention.

FIGURE 2 is an enlarged vertical cross section of another embodiment of this invention.

FIGURE 3 is a side elevation of FIGURES 1 and 2, and showing in actual scale the extremely small size of the fuse control.

FIGURE 4 is an enlarged exploded perspective view showing the parts of the embodiment of FIGURE 1, and also being substantially a suitable illustration for the internal parts of FIGURE 2.

FIGURE 5 shows line conductors with heads at their lower ends, which conductors may be used in either of the embodiments of FIGURES 1 or 2.

FIGURE 6 is a cross section along line 6-6 of FIGURE 5.

FIGURE 7 is a diagrammatic vertical cross section of a portion of an apparatus for practicing the method of assembly of this invention.

Certain words are used in this specification and in the appended claimed subject matter, which indicate direction, relative position, and the like. Such words are used for the sake of clearness, and brevity. However, it is to be understood that such words are used only in connection with the illustrations in the drawings, and are not intended to apply to the actual devices when in use. Such directions, and relative positions, etc., obviously can be different in the devices when in actual use. Examples of such words are horizontal, vertical, upper, etc.

According to this invention, a fuse control may be made of extremely small size, such as of the size indicated in FIGURE 3.

Such control may have a metallic cup-shaped casing 10 having a horizontal bottom 12, a cylindraceous, or cylindrical, side wall 14, and an upper inward flange 16. A thermally collapsible pellet 18 may be placed adjacent the bottom 12. Such pellet 18 may be cylindraceous, or cylindrical in shape, with parallel upper and lower sides. The material of such pellet may be any of the materials now commonly used by manufacturers of such pellets, which pellets are available on the market throughout the United States. The compositions of such pellets are well known to the manufacturers thereof, and such com- "ice positions form no part of this invention. Many patents relating to fuse controls disclose various compositions which may be used for such pellets, and hence it is believed unnecessary to disclose, in this application, any particular composition for pellets. In general, these pellets are of a nature that they remain in substantially solid form until a certain critical relatively high :temperature is reached. When such relatively high temperature is reached, they quickly collapse, and become fluid within a very narrow temperature range. When they become fluid, they allow the parts of the fuse control to move to other positions, and thus to change the current carrying characteristics of the fuse control.

If desired, a relatively rigid disc 20 may be placed on the upper surface of the pellet 18, to distribute a spring pressure imposed thereon throughout the entire upper surface of said pellet.

A relatively strong, vertical, compression coil spring 22 may have its lower end exerting a downward pressure on the pellet 18. As stated, such pressure may be distributed substantially throughout the area of the pellet 18 by interposing the relatively rigid disc 20 between the lower end of the spring 22, and the upper surface of the pellet 18.

A hat-shaped member 24 may have an upper crown 26, a vertical cylindraceous or cylindrical wall 28 and a lower outward rim 30. The interior of the crown 26 may receive the upper end of the strong spring 22. If desired, the strong spring 22 may be slightly relatively narrower at its lower end, and relatively wider at its upper end, so that it can freely expand telescoped within the cylindical wall 28 when such spring is compressed into position.

A relatively weak, vertical, compression coil spring 32 may have its lower end engaging the rim 30 of the hat-shaped member 24.

A relatively rigid, insulator cover member 34 may be substantially disc-shaped, and may be placed in the casing 10 with its edge 36 to be engaged by the under side of the later formed inward flange 16 and with the under side of said disc 34 engaging the upper end of the relatively Weak spring 32.

The relatively weak spring 32 may have its upper end relatively wide, and its lower end relatively narrow, to produce a relatively straight axial thrust on the hatshaped member 24, and to prevent shorting of the two line conductors 38 and 40, when the pellet 18 collapses.

The two vertical line conductors 38 and 40 may pass through the insulator cover 34 and may have their lower ends engaging the crown 26 when the pellet 18 is not collapsed, such as shown in FIGURES 1 and 2. However, when the pellet 18 collapses, the relatively weak spring 32 moves the hat-shaped member 24, with its crown 26, downwardly away from the lower ends of the line conductors 38 and 40, and this action breaks the electric circuit which previously had been passing from one conductor, such as 38, through the crown 26, to the other conductor 40.

The top of the crown 26 may be flat, and the lower ends of the conductors 38 and 40 may be flat, as shown in the drawings, in all the FIGURES 1, 2, 5 and 6.

In the embodiment shown in FIGURE. 1, a vertical cylindraceous or cylindrical insulative sleeve 42 may be placed in the casing 10 with the sleeve upper end 44 engaging the lower side of the insulator cover member 34, and with the lower end 46 engaging the horizontal bottom 12 of the casing 10.

The insulative sleeve 42 may be made of thermally resistant glass, ceramic material, or the like. The sleeve 42 may have a cyl-indraceous or cylindrical side wall 48, which may be adjacent to the cylindrical or cylindraceous .3) side wall 14 of the casing 10. The wall 48 may surround the components that may be desired to be placed in the main body of the fuse control, as illustrated in FIGURES 1 and 4.

In the embodiment of FIGURE 2, all of the parts heretofore described in connection with FIGURE 1 may be the same, or substantially the same, when used in the embodiment of FIGURE 2, with the exception that the insulative sleeve 42, 48 of FIGURES 1 and 4 is omitted in FIGURE 2. Also, if desired, the cylindraceous or cylindrical side wall 14A of FIGURE 2 may be slightly thicker than the Wall 14 of FIGURE 1. The side wall 14A may be provided with an outward or transverse shoulder 50 spaced from but near the inward flange 16A. The edge 36A of the cover member 34A may be held between the shoulder 50 and the flange 16A, to maintain the insulator cover member 34A securely held between the shoulder 50, and the flange 16A. The flange 16A is formed from its initially cylindrical form to its inward flange form after the cover member 36A has been placed on the shoulder 50.

All of the components disclosed in FIGURE 2, which have the same reference characters as those of FIGURE 1, have the suffix A added thereto and may have the same construction and function in FIGURE 2, that they have in FIGURE 1. Therefore, such reference characters with the suflix A have been added to FIGURE 2, but description thereof may not be repeated, unless it is deemed necessary, in connection with FIGURE 2, since it is obvious that they may have the same structure and function as in FIGURE 1. It is thus to be understood that all of the parts of FIGURE 2 may be substantially the same as in FIGURE 1, with the same function, with the exception that the insulative sleeve 42, 48 of FIG- URES 1 and 4 is omitted in FIGURE 2, and that, if desired, the side wall 14A of FIGURE 2 may be made thicker than the side wall 14 of FIGURE 1.

If desired, the lower ends of the conductors 38, 40, 38A, 40A, may be provided with wider heads 52, as shown in FIGURES 5 and 6. Such heads may be formed from the ends of such conductors, and the conductors may be inserted into the insulator cover member 34, or 34A, upwardly, before the cover member 34 or 34A is inserted in the casing 10. The heads 52 may be shaped as shown in FIGURE 6 so they have large contact areas with the crown 26, but do not protrude materially beyond the edge of the crown 26. After such conductors have been inserted upwardly in the cover member 34, or 34A, such conductors may be sealed or adhesively connected to such cover members 34 or 34A by any suitable sealing compound, such as an epoxy resin adhesive or compound, or the like. After these conductors have been so secured within the cover members 34 or 34A, such cover members with the conductors therein, may be inserted into the casing 10, before the flange 16 is formed thereon, and then the flange 16 may be pressed down and formed inwardly by a suitable press action or rolling action, as desired. In the case of FIG- URE l, the edge 36 of cover member 34 is placed on the top end of insulative sleeve 48 and then the flange 16 is formed inwardly over the upper surface of the cover member 34. In the case of FIGURE 2, the edge 36A of cover member 34A is placed over the transverse shoulder 50, and then the flange 16A is formed inwardly over the top surface of the cover member 34A.

The fuse construction of this invention may be very 'efliciently maufactured by providing a horizontal flat assembly member 60, FIGURE 7, with suitable openings 62 in its upper surface capable of receiving a large number of casings 10, before they are flanged, as shown at 64, FIGURE 7. Thereafter, the desired components may be assembled downwardly into the casings 10, in the upward order shown in FIGURE 4 starting with insulative sleeve 42, pellet 18, etc., with respect to FIGURE 1. The embodiment of FIGURE 2 may be similarly assembled by placing the cylindrical casings 14A with unflanged upper ends in the openings 62, and then the internal components of FIGURE 4 may be inserted in the same order, with the omission of the sleeve 42, for the construction of FIG- URE 2.

If desired, the openings 62 in the assembly member 60 may be slightly shorter than the length of the casing 10, and after the members have been so assembled, with the conductors 38, 40, 38A and 40A having first been assembled within the cover members 34 and 34A, then the flange 16, or 16A, as the case may be, may be inwardly formed or pressed, as shown at 66, FIGURE 7, to complete the assembly of the fuse controls. Thereafter, each completed control member may be lifted out of its respective opening and will be ready for use.

Alternatively, only some of the components may be assembled in the openings 62 of the horizontal member 60, and then such partial assemblies may be removed and completed outside of said openings 62.

The external diameter of the casing 10 may be in the order of A of an inch, more or less, and the length of such casing 10 may be proportionately only slightly longer than A; of an inch, as is indicated by the relative proportions of width and length in the drawings of this application.

Embodiments of this invention have been made and have a safe capacity to carry a 2 ampere current with the sizes herein given.

If desired, the conductors 38, 40, 38A and 40A, and/ or the hat-shaped member 24 may be made of silver plated copper, solid silver, gold, or any other base metal or alloy with suitable conductivity and suitable minimum contact resistance characteristics. Such metal construction may be used to increase the conductivity between the ends of the conductors and the hat-shaped member 24, so that the current from one conductor to the other may have a minimum resistance imposed thereon.

It is thus to be seen that a new, useful and unobvious fuse construction has been provided.

While the form of the invention now preferred has been disclosed as required by statute, other forms may be used, all coming within the scope of the claimed subject matter which follows.

What is claimed is:

1. In combination, in a miniature fuse: a metallic cupshaped casing having a horizontal bottom, a cylindraceous side wall, an upper inward flange and a transverse shoulder adjacent said inward flange; a thermally collapsible pellet adjacent said bottom; a relatively strong vertical compression coil spring with its lower end exerting a downward pressure on said pellet; a hat-shaped member having a crown, a vertical cylindraceous wall, and a rim, with said crown on and receiving the upper end of said strong spring within said crown; a relatively weak vertical compression coil spring with its lower end on said rim of said hat-shaped member; a relatively rigid insulator cover member in said casing with the top of its edge engaging the under side of said inward flange, and with its under side engaging said transverse shoulder and the upper end of said relatively weak spring; two vertical line conductors passing through said insulator cover member and having lower ends engaging said crown when said pellet is not collapsed, said relatively weak spring moving said crown away from said ends of said line conductors when said pellet is thermally collapsed, the top of said crown being flat and receiving the upper end of said strong spring, the lower ends of said conductors being flat, said weak spring being relatively wider at its upper end and relatively narrower at its lower end, said weak spring being held spaced from said conductors by said wider upper end against said insulator cover member and by said narrower lower end against said rim.

2. In combination, in a miniature fuse: a metallic cupshaped casing having a horizontal bottom, a cylindraceous side wall and an upper inward flange; a thermally collapsible pellet adjacent said bottom; a relatively strong vertical compression coil spring with its lower end exerting a downward pressure on said pellet; a hat-shaped member having a crown, a vertical cylindraceous wall, and a rim, with said crown on and receiving the upper end of said strong spring within said crown; a relatively weak vertical compression coil spring with its lower end on said rim of said hat-shaped member; a relatively rigid insulator cover member in said casing with its edge engaging the under side of said inward flange and with its under side engaging the upper end of said relatively weak spring; two vertical line conductor-s passing through said insulator cover member and having lower ends engaging said crown when said pellet is not collapsed, said relatively weak spring moving said crown away from said ends of said line conductors when said pellets is thermally collapsed; and a vertical cylindraceous insulative sleeve located in said cup-shaped casing which sleeve has an upper end and a lower end with said lower end engaging said horizontal bottom and said upper end engaging said lower side of said insulator cover member, said insulative sleeve being adjacent said cylindraceous side wall of said casing and surrounding :said pellet, said strong spring, said hat-shaped member, and said weak spring.

References Cited by the Examiner UNITED STATES PATENTS 2,127,648 8/1938 Mehlhouse 29-155 2,931,874 4/1960 Leaman 200-142 2,934,628 4/1960 Massar et a1. 200-142 2,955,179 10/1960 Milton et al 200-142 3,167,852 2/1965 Stengl 29-155 3,178,540 4/1965 Gay 61. a1. 200142 3,180,958 4/1965 Merrill 200142 3,221,225 11/1965 Sternbeck 2001 17 BERNARD A. GILHEANY, Primary Examiner. H. B. GILSON, Assistant Examiner. 

1. IN COMBINATION, IN A MINIATURE FUSE: A METALLIC CUPSHAPED CASING HAVING A HORIZONTAL BOTTOM, A CYLINDRACEOUS SIDE WALL, AN UPPER INWARD FLANGE AND A TRANSVERSE SHOULDER ADJACENT SAID INWARD FLANGE; A THERMALLY COLLAPSIBLE PELLET ADJACENT SAID BOTTOM; A RELATIVELY STRONG VERTICAL COMPRESSION COIL SPRING WITH ITS LOWER END EXERTING A DONWARD PRESSURE ON SAID PELLET; A HAT-SHAPED MEMBER HAVING A CROWN, A VERTICAL CYLINDRACEOUS WALL, AND A RIM, WITH SAID CROWN ON AND RECEIVING THE UPPER END OF SAID STRONG SPRING WITHIN SAID CROWN; A RELATIVELY RIGID VERTICAL COMPRESSION COIL SPRING WITH ITS LOWER END ON SAID RIM OF SAID HEAT-SHAPED MEMBER; A RELATIVELY RIGID INSULATOR COVER MEMBER IN SAID CASING WITH THE TOP OF ITS EDGE ENGAGING THE UNDER SIDE OF SAID INWARD FLANGE, AND WITH ITS UNDER SIDE ENGAGING SAID TRANSVERSE SHOULDER AND THE UPPER END OF SAID RELATIVELY WEAK SPRING; TWO VERTICAL LINE CONDUCTORS PASSING THROUGH SAID INSULATOR COVER MEMBER AND HAVING LOWER ENDS ENGAGING SAID CROWN WHEN SAID PELLET IS NOT COLLAPSED, SAID RELATIVELY WEAK SPRING MOVING SAID CROWN AWAY FROM SAID ENDS OF SAID LINE CONDUCTORS WHEN SAID PELLET IS THERMALLY COLLAPSED, THE TOP OF SAID CROWN BEING FLAT AND RECEIVING THE UPPER END OF SAID STRONG SPRING, THE LOWER ENDS OF SAID CONDUCTORS BEING FLAT, SAID WEAK SPRING BEING RELATIVELY WIDER AT ITS UPPER END AND RELATIVELY NARROWER AT ITS LOWER END, SAID WEAK SPRING BEING HELD SPACED FROM SAID CONDUCTORS BY SAID WIDER UPPER END AGAINST SAID INSULATOR COVER MEMBER AND BY SAID NARROWER LOWER END AGAINST SAID RIM. 